USA Payment Gateway Implementation

I'm seeking an experienced developer to implement a new payment gateway in the USA, specifically for processing online payments. We have this gateway available in some other countries and want to implement in USA

Key requirements:
- Expertise in payment gateway integration
- Familiar with security protocols and compliance standards
- Experience with either PayPal, Stripe, or Square

Ideal skills and experience:
- Proven track record in similar projects
- Strong technical background
- Ability to document the integration process

Please provide a portfolio with relevant experience.